Six years ago Ken Mehlman was running the re-election campaign of a president who sought a constitutional amendment to ban same-sex marriage.

Now he's the nation's most prominent openly gay Republican and the latest member of the George W. Bush administration to support extending marriage rights to gays and lesbians.

Mehlman has been working as a fundraiser and strategist for the American Foundation for Equal Rights -- a group that supports same-sex marriage and is suing to overturn California's Proposition 8.

Play

Former Bush Campaign Manager Ken Mehlman Announces He's Gay

"In the context of doing that, some questions had come up and I wanted to answer the questions honestly," Mehlman told ABC News following his decision to reveal his sexual orientation in an interview with The Atlantic.

"When I was at the RNC I hadn't come to terms with it, I hadn't accepted it," he said. "My family and my friends found out about this in the last several months."

But whether Mehlman's high-profile outing and support for gay marriage will trigger a broader shift within the GOP is far from certain. The party's official 2008 platform still calls for a constitutional amendment to define marriage between a man and a woman.

And some of the early possible contenders for the Republican nomination in 2012 – including former Alaska Gov. Sarah Palin, Minnesota Gov. Tim Pawlenty, former Massachusetts Gov. Mitt Romney, and former Arkansas Gov. Mike Huckabee – all oppose gay marriage.

Play

Gay Marriages Temporarily on Hold in California

"I accepted his decision," former RNC chair Ed Gillespie said on "Good Morning America." "We agreed to disagree on the issue of same-sex marriage. But proponents of same-sex marriage within the Republican Party have gained an effective advocate."

Still, Mehlman's outing and newfound support for gay marriage rights is drawing criticism from some corners because of his history of opposing gay rights while simultaneously leading a double life.

"Ken Mehlman was going to low-profile gay parties. Ken Mehlman was dating men. Ken Mehlman was going to a predominantly gay gym. Ken Mehlman was living the life of a gay man, albeit deeply in the closet. He knew who he was," said liberal gay blogger Mike Rogers, who outed Mehlman years ago online.

Play

Same-Sex Marriages on Hold in California

"It was on the backs of the very people who Ken Mehlman now wants to be welcomed into as a community that he built his political career," he said.

Mehlman Regrets Not Coming Out Earlier

Mehlman told NBC's Tim Russert in 2005, "The president strongly believes that marriage in this country ought to be between a man and a woman...He believes that a constitutional amendment is appropriate so the people can weigh in."

Play

Judge Overturns Prop 8 Gay Marriage Ban in California

He also questioned the nature of homosexuality, which is often at the heart of opponents arguments against gay rights.

"Do you believe homosexuality is a choice?" Russert asked Mehlman in the 2005 interview.

"I don't know the answer to that question," he said.

Mehlman has since insisted he could not, as one individual, go against the party consensus on marriage and he doesn't believe the marriage debate was a deciding factor in the 2004 presidential election.

He also said some gay marriage opponents' views are genuinely and deeply held. "It's a mistake to assume to those who disagree on the right to marry issue are motivated by bigoted feelings," he said. "A lot of the friends I have who feel differently on that issue are motivated by heartfelt belief. I look forward to trying to persuade them on my own views but I think it's a mistake to question their motives."

Play

California Judge Overturns Gay Marriage Ban

Does he regret being part of that campaign in any way?

"No," Mehlman said. "What I regret is the fact that I had not come to terms with this part of my life and therefore...I was not able to do what I was able to do in other areas and work for a more inclusive and broader party."

Former Republican Senate staffer John Reid, who was also outed by Rogers, says he's hopeful Mehlman's admission now will make a difference in the way the party treats gays.

"Suddenly Republican activists and Republican politicians are faced with the reality that they know good, gay people," he said. "And it's a lot harder to speak out against good, strong individuals when you actually know that they're close to you and they're working for the same ultimate goals within your party."